EXPLANATION. OF PLATES XV 



PLATE VI. (Facing p. 550) 



SEXUAL GENERATION OF VOLVO X GLOBATOR. (After Collll) 



Fig. 1. Sphere of Volvox globator at the epoch of sexual generation : . 

 sperm-cell containing cluster of antherozoids ; .'-', sperm-cell showing side- 

 view of discoitlal cluster of antherozoids ; a 3 , sperm cell whose cluster has 

 broken up into its component antherozoids ;', sperm-cell partly emptied by 

 the escape of its antherozoids; bb, flask-shaped germ-cells showing great 

 increase in size without subdivision ; b'-, b' 2 , germ-cells with large vacuoles in 

 their interior ; b 3 , germ-cell whose shape has changed to the globular. 



Fig. 2. Sexual cell, a, distinguishable from sterile cells, b, by its larger 

 size. 



Fig. 3. Germ-cell, with antheroids swarming over its endochrome. 



Fig. 4. Fertilised germ-cell, or oosphere, with dense envelope. 



Fig. 5. Sperm-cell, with its contained cluster of antherozoids, more 

 enlarged. 



Figs. 6, 7. Liberated antherozoids, with their flagella. 



PLATE VII. (Facing p. 553) 



OSCILLAKIACEJE AND SCYTONEMACE^E 



Fig. 1. Li/ngbya H'stunrii. Lieb. >. 160. 



Fig. 2. Spii-nUna Jcnneri, Ktz. : 400. 



Fig. 3. Tolypotliri.r cirrliosa, Carm. : 400. 



Fig. 4. OsciUaria insignis, Thw. 400. 



Fig. 5. 0. FroUcJiii, Ktz. x 400. 



Fig. 6. 0. tcncrriina, Ktz. x 400. 

 These figures are after Cooke. 



PLATE VIII. (Facing p. 554) 

 DESMIDIACE.E, RIVULARIACE^, AND SCYTONEMACE.E 



Fig. 1. Zygosperm of Micrasterias denticulata, Breb. (After Ealfs.) 



Fig. 2. Cosmarium Brebissonii, Men. (After Cooke.) 



Fig. 3. Euastrum pectinatuin, Breb. (After Kalf s.) 



Fig. 4. Zygosperm of Staurastrum hirsutum, Breb. (After Ealfs.) 



Fig. 5. S. gracile, Ealfs. (After Cooke.) 



Fig. G. Xaniliidium aculeatum, Ehrb. (After Ealfs.) 



Fig. 7. Rivularia dura, Ktz. (After Cooke.) 



Fig. S. R. dura, Ktz. x 400. (After Cooke.) 



Fig. 9. Seytonema natans, Breb. : : 400. (After Cooke.) 



Fig. 10. Stawastrum hirsutum, Breb. (After Cooke.) 



PLATE IX. (Facing p. 580) 

 DESMIDIACEJE 



Fig. 1. Micrasterias cnix-meliteiisis, Ehrb. (After Cooke.) 



Fig. 2. Clostcrium setaceum, Ehrb. (After Cooke.) 



Fig. 3. Desmidium Sivartzii, Ag. (After Cooke.) 



Fig. 4. Penium digitus, Ehrb. (After Cooke.) 



Fig. 5. P. digitus, Ehrb. (transverse view). 



Fig. 6. Spirot<cnia condensata, Breb. (After Cooke.) 



Fig. 7. Docldium baculum, Breb. (After Cooke.) 



Fig. 8. Gonatozygon Brebissonii, De Bary, conjugating. (After Cooke.) 



PLATE X. (Facing p. 5U3) 



PLEUROSIGMA ANGULATUM 



This is a direct photo-micrograph, taken by Dr. E. Zeiss, as magnified 4900 

 diameters. We direct attention specially to it as giving evidence of the pre- 

 sence (however originated) of the intercostal markings, which may be seen 

 with considerable clearness on the right-hand side of the midrib and in the 

 middle of the valve. 



